Importance of advection for pelagic-benthic coupling in north Norwegian fjords

Suspended biomass in the upper layer and sedimentation of organic matter were measured during spring and early summer simultaneously in Balsfjord and Malangen, northern Norway (ca 70° N) in 1992 at four different depths ranging from 30 to 170 m and 330 m, respectively. The bloom took place in almost unstratified waters in April and was dominated by diatoms and Phaeocystis pouchetii, Hariot. The biomass of the early bloom was exported from the fjord due to advection, resulting in low sedimentation rates in the fjord. Several advective episodes were observed during the course of the bloom. These were caused by large scale variation in the wind field along the coast. The bloom continued until the end of April with high POC fluxes ranging from 300-1120 mg m-2 day-1 at all depths. Suspended POC in the upper 36 m was high, varied between 16 and 31 g m-2 day-1 and was not correlated to the phytoplankton bloom. It is suggested that topographical controlled down-fjord wind stress during periods of low stratification gives rise to extensive water circulation and resuspension, in particular in narrow fjords. Advection of zooplankton into the fjords influences the vertical flux by introduction and removal of specific zooplankton stocks. The results imply that advection is a significant process for the development and fate of vernal blooms in north Norwegian fjords and that vernal blooms and pelagicbenthic coupling will be subjected to interannual variation due to variable meteorological forcing.